1. The Field of The Invention
This invention relates to means for distributing hot gas on a moving sheet of paper.
2. State of the Art
In most paper products it is desirable to automatically control the cross machine moisture content using a steam shower or steam distributor. Most paper machines have continuous moisture scanners which read the sheet moisture content across the machine as the paper is manufactured. The information from this continuous measurement can be fed into a controlling computer and the steam flow in the steam distributor can be automatically controlled according to this information.
One type of steam distributor is taught in U.S. Pat. No. 4,253,247. The patent teaches a multi-chambered steam hood with means of steam distribution to each chamber provided by a steam distributor. Steam flows from the steam distributor through ports into a nozzle and into each chamber. The steam flow is controlled by raising or lowering a control plug.
According to the patent the plug has a piston ring located around its periphery. It is believed that a piston ring in such a location would substantially prevent any flow of steam into the chamber when the plug is in the closed position. This could lead to cooling of parts of the chamber and condensation of steam to liquid water therein. The liquid water could drop from the chamber onto the paper thereby producing local discoloration called streaking.